1. Field of the Invention
The invention in general relates to high dielectric constant materials for use in integrated circuits, and more particularly to integrated circuits incorporating thin films of barium-strontium-niobium oxides.
2. Statement of the Problem
It is well-known that there is a need for a high dielectric constant material suitable for use in integrated circuits. The most commonly used dielectric material in integrated circuits is silicon dioxide, which has a dielectric constant of about 4. Capacitors using such a material must have a large area in order to provide the capacitive values required in state-of-the-art integrated circuits. These large areas make it difficult to reach high densities of capacitive components in an integrated circuit. However, the use of other materials to provide the dielectric in integrated circuits has been hindered by the fact that materials with high dielectric constants usually have many problems such as: leakage of the dielectrics in the integrated circuit environment, degradation and breakdown of the materials caused by the stresses of fabrication and use over long time periods, and incompatibility of the materials with other common integrated circuit materials. For example, lead-zirconate-titanate, usually called PZT, a well-known material used in ferroelectric integrated circuits has a dielectric constant of about 800, but also contains lead, which tends, over time, to migrate to the silicon semiconducting portions of the integrated circuits, causing alteration of their semiconducting properties. Thus, the presence of lead in combination with conventional integrated circuit materials significantly reduces the long-term reliability of the integrated circuit. Barium strontium titanate has also been successfully used in an integrated circuit, but its dielectric constant is not as high as PZT. Titanium also has a large number of oxidation states which can, under certain conditions lead to defects in the crystal structure that can degrade the electrical performance of the material. As integrated circuits become smaller, it becomes more and more important to find a dielectric material that has a dielectric constant of 500 or more, but does not contain problematic elements. The lack of such a material is considered to be one of the serious roadblocks to higher density integrated circuit memories.
3. Solution to the Problem
The present invention solves the above problem by providing an integrated circuit incorporating an oxide of barium, strontium and niobium. Preferably the barium-strontium-niobium oxide is Ba.sub.2 Sr.sub.3 Nb.sub.10 O.sub.30. Not only is the dielectric constant very high, but the leakage current is very low, indicating that it will perform well in a charge storage device, such as an integrated circuit memory, and as an insulator between conductive elements of the integrated circuit. Other formulations of BSN, such as Ba.sub.1.3 Sr.sub.3.7 Nb.sub.10 O.sub.30, have also been found to have a high-dielectric constant and good electronic properties. Thus, there is a range of proportions of barium and strontium that provides high dielectric constant and good electronic properties. In this disclosure, we shall refer to the foregoing materials, and any metal oxide in which the metals are primarily barium, strontium, and niobium, as BSN. BSN is intended to include materials that are doped with smaller amounts of other elements; that is, the molecular amount of the dopant element is less than the molecular amount of either barium, strontium, or niobium in the BSN.
The preferred BSN material according to the invention has a dielectric constant of over 500 for all frequencies and nearly 1300 at low frequencies. In addition, it has a leakage current of less than 10.sup.-5 amps per square centimeter for a film thickness of about 1600 angstroms and voltages of up to five volts. It does not include any materials that are known to be incompatible with conventional integrated circuit materials or which have properties that can degrade the performance of the material. While the excellent properties of the material and the ability to make very thin films of the material that retain those properties make the invention of particular importance for integrated circuits. However, it also is of importance for any type of charge storage device. Numerous other features, objects and advantages of the invention will become apparent from the following description when read in conjunction with the accompanying drawings.